LED driver for VLC

Abstract

A visual light communication (VLC) method for a lighting system comprising an LED driver and a plurality of LEDs or LED groups includes the steps of: receiving a set-point representing a desired illumination characteristic, comprising an intensity set-point, a color set-point or a combination thereof, and data that is to be transmitted using VLC; determining a current profile for each LED or LED group of the plurality of LEDs or LED groups based on the desired illumination characteristic represented by the set-point, whereby an envelope of a combined current profile is modulated for a corresponding intensity variation as perceived by a sensor to represent a variable length VLC code comprising one or more code words; and generating one or more control signals to drive the plurality of LEDs or LED groups in accordance with the current profiles for the plurality of LEDs or LED groups to transmit the VLC code.

The invention claimed is: 
     
       1. A visual light communication (VLC) method for a lighting system comprising an LED driver and a plurality of LEDs or LED groups, the method comprising the steps of:
 receiving a set-point representing a desired illumination characteristic of the plurality of LEDs or LED groups in a VLC mode, comprising an intensity set-point and a color set-point, and data that is to be transmitted in the VLC mode; 
 determining a current profile for each LED or LED group of the plurality of LEDs or LED groups based on the desired illumination characteristic represented by the set-point, whereby an envelope of a combined current profile of the current profiles is configured to represent one or more code words comprising a plurality of symbols and is modulated in order for a corresponding intensity variation as perceived by a sensor to represent a variable length VLC code representing the data for transmission, the VLC code comprising the one or more code words, a code word comprising the plurality of symbols, whereby each of the plurality of symbols is characterized by both a respective predetermined period and the received set-point of the desired illumination characteristic, and whereby the current profile for each of the LED or LED groups is determined in such a manner that the illumination as generated by the plurality of LEDs or LED groups in the VLC mode corresponds to the desired illumination characteristic; and 
 generating one or more control signals to drive the plurality of LEDs or LED groups in accordance with the envelope of the combined current profiles in order for the plurality of LEDs or LED groups to transmit the VLC code such that each of the plurality of symbols of the one or more code words transmitted as the data in the envelope of the combined current profiles is identified based only on the duration of the predetermined period and the intensity variation of the plurality of LEDs or LED groups corresponding to the desired illumination characteristic applied during the data transmission, 
 wherein the combined current profile has a high current period and a low current period during each predetermined period, 
 wherein each predetermined period represents a single symbol. 
 
     
     
       2. The visual light communication method according to  claim 1 , wherein the step of determining the current profile for each of the plurality of LEDs or LED groups comprises determining a modulated current profile for at least one LED or LED group of the plurality of LEDs or LED groups. 
     
     
       3. The visual light communication method according to  claim 2 , wherein a modulation of the combined current profile corresponds to a modulation of the modulated current profile for the at least one LED or LED group of the plurality of LEDs or LED groups. 
     
     
       4. The visual light communication method according to  claim 2 , wherein the plurality of LEDs or LED groups comprise LEDs or LED groups having a different color and the at least one LED or LED group of the plurality of LEDs or LED groups is selected based on the data. 
     
     
       5. The visual light communication method according to  claim 1 , wherein the combined current profile comprises a summation of the current profiles of the plurality of LEDs or LED groups. 
     
     
       6. The visual light communication method according to  claim 1 , wherein the data is encoded in the envelope of the combined current profile. 
     
     
       7. The visual light communication method according to  claim 1 , whereby a symbol is characterized by both the predetermined period and a color or color range. 
     
     
       8. The visual light communication method according to  claim 7 , wherein the color range comprises a plurality of distinct ranges. 
     
     
       9. The visual light communication method according to  claim 8 , wherein the distinct ranges correspond to areas in a CEI chromaticity diagram or correspond to segments of a contour in the CEI chromaticity diagram. 
     
     
       10. The visual light communication method according to  claim 8 , wherein the step of determining the current profile for each LED or LED group of the plurality of LEDs or LED groups further comprises selecting a color for transmitting a symbol of a code word of the VLC code from the plurality of distinct ranges based on a received color set point and an average color generated during a predetermined period prior to transmitting the symbol. 
     
     
       11. The visual light communication method according to  claim 8 , further comprising determining a moving average color as the average color transmitted during a predetermined previous period and selecting a color for transmitting a symbol of a code word of the VLC code from the plurality of distinct ranges based on a received color set point and the moving average color. 
     
     
       12. The visual light communication method according to  claim 7 , further comprising applying a color compensation scheme after transmitting one or more code words, based on a received color set point. 
     
     
       13. The visual light communication method according to  claim 1 , further comprising the steps of:
 receiving a further set-point representing a different desired illumination characteristic, 
 determining a further current profile for one or more of the plurality of LEDs to generate the different desired illumination characteristic represented by the further set-point, and 
 determining one or more intermediate current profiles for one or more of the plurality of LEDs, and determining output control signals for the LED driver to sequentially drive the plurality of LEDs or LED groups according to: 
 the current profiles when transmitting a first code word; 
 the one or more intermediate current profiles, when transmitting a respective one or more further code words, and 
 the further current profiles when transmitting a yet further code word. 
 
     
     
       14. An LED driver for driving a plurality of LEDs or LED groups to transmit light in a VLC mode, wherein the LED driver comprises a control unit that is configured to perform the method according to  claim 1 . 
     
     
       15. An LED driver for driving a plurality of LEDs or LED groups to transmit light in a VLC mode, wherein the LED driver comprises a control unit that is configured to:
 receive, at an input terminal, a set-point representing a desired illumination characteristic of the plurality of LEDs or LED groups, comprising an intensity set-point and a color set-point, and data that is to be transmitted in the VLC mode; 
 determine a current profile for each LED or LED group of the plurality of LEDs or LED groups based on the desired illumination characteristic represented by the set-point, whereby an envelope of a combined current profile of the current profiles is configured to represent one or more code words comprising a plurality of symbols and is modulated in order for a corresponding intensity variation as perceived by a sensor to represent a variable length VLC code representing the data for transmission, the VLC code comprising the one or more code words, a code word comprising the plurality of symbols, whereby each of the plurality of symbols is characterized by both a respective predetermined period and the received set-point of the desired illumination characteristic, and whereby the current profile for each of the LED or LED groups is determined in such a manner that the illumination as generated by the plurality of LEDs or LED groups in the VLC mode corresponds to the desired illumination characteristic; and 
 generate one or more control signals to drive the plurality of LEDs or LED groups in accordance with the envelop of the combined current profiles in order for the plurality of LEDs or LED groups to transmit the VLC code such that each of the plurality of symbols of the one or more code words transmitted as the data in the envelope of the combined current profiles is identified based only on the duration of the predetermined period and the intensity variation of the plurality of LEDs or LED groups corresponding to the desired illumination characteristic applied during the data transmission, 
 wherein the combined current profile has a high current period and a low current period during each predetermined period, 
 wherein each predetermined period represents a single symbol. 
 
     
     
       16. The LED driver according to  claim 15 , wherein the control unit is configured to determine a modulated current profile for at least one LED or LED group of the plurality of LEDs or LED groups. 
     
     
       17. The LED driver according to  claim 16 , wherein a modulation of the combined current profile corresponds to a modulation of the modulated current profile for the at least one LED or LED group of the plurality of LEDs or LED groups. 
     
     
       18. The LED driver according to  claim 17 , wherein the combined current profile comprises a summation of the current profiles of the plurality of LEDs or LED groups. 
     
     
       19. The LED driver according to claim according to  claim 15 , wherein the data is encoded in the envelope of the combined current profile. 
     
     
       20. The LED driver according to claim according to  claim 15 , whereby a symbol is characterized by both the predetermined period and a color or color range. 
     
     
       21. The LED driver according to claim according to  claim 20 , wherein the color range comprises a plurality of distinct ranges. 
     
     
       22. The LED driver according to claim according to  claim 21 , wherein the distinct ranges correspond to areas in a CEI chromaticity diagram or correspond to segments of a contour in the CEI chromaticity diagram. 
     
     
       23. The LED driver according to  claim 21 , whereby the step of determining the current profile for each LED or LED group of the plurality of LEDs or LED groups by the control unit further comprises selecting a color for transmitting a symbol of a code word of the VLC code from the plurality of distinct ranges based on a received color set point and an average color generated during a predetermined period prior to transmitting the symbol. 
     
     
       24. The LED driver according to claim according to  claim 23 , wherein the control unit is further configured to determine a moving average color as the average color transmitted during a predetermined previous period and to select a color for transmitting a symbol of a code word of the VLC code from the plurality of distinct ranges based on a received color set point and the moving average color. 
     
     
       25. The LED driver according to  claim 15 , wherein the control unit is further configured to receive a color set point and apply a color compensation scheme after a transmission of one or more code words, based on the received color set point. 
     
     
       26. The LED driver according to  claim 15 , wherein the control unit is further configured to:
 upon receipt of a further set-point representing a different illumination characteristic during the transmission of the VLC code, determine an adjusted current profile or profiles for one or more of the plurality of LEDs or LED groups based on the different illumination characteristic, whereby the current profile is only adjusted for some, not all, symbols of a next code word to be transmitted; 
 generate one or more control signals to drive the plurality of LEDs or LED groups in accordance with the adjusted current profile or profiles, and 
 output, via an output terminal of the control unit, one or more control signals to drive the plurality of LEDs or LED groups in accordance with the adjusted current profile or profiles. 
 
     
     
       27. The LED driver according to  claim 26 , wherein the LED driver is configured to adjust a current for any LED of the plurality of LEDs or LED groups at a plurality of discrete values at a plurality of discrete instants. 
     
     
       28. The LED driver according to  claim 27 , wherein the LED driver is configured to adjust the current profile of only one symbol of a next code word with a minimum current increment per instant. 
     
     
       29. The LED driver according to  claim 28 , wherein each symbol is characterized by a predetermined period and at least two different intensities applied during the predetermined period. 
     
     
       30. A control unit for controlling an LED driver to drive a plurality of LEDs or LED groups to transmit light in a VLC mode, the control unit comprising:
 an input terminal configured to receive a set-point representing a desired illumination characteristic of the plurality of LEDs or LED groups, comprising an intensity set-point and a color set-point, and data that is to be transmitted in the VLC mode; and 
 an output terminal configured to output one or more control signals for controlling the LED driver, 
 the control unit being configured to: 
 determine a current profile for each LED or LED group of the plurality of LEDs or LED groups to generate the desired illumination characteristic represented by the set-point, whereby an envelope of a combined current profile is configured to represent one or more code words comprising a plurality of symbols and is modulated in order for a corresponding intensity variation as perceived by a sensor to represent a variable length VLC code representing the data for transmission, the VLC code comprising the one or more code words, a code word comprising the plurality of symbols, whereby each of the plurality of symbols is characterized by both a respective predetermined period and the received set-point of the desired illumination characteristic, and whereby the current profile for each of the LED or LED groups is determined in such a manner that the illumination as generated by the plurality of LEDs or LED groups in the VLC mode corresponds to the desired illumination characteristic; and 
 generate one or more control signals to drive the plurality of LEDs or LED groups in accordance with the envelope of the combined current profiles in order for the plurality of LEDs or LED groups to transmit the VLC code such that each of the plurality of symbols of the one or more code words transmitted as the data in the envelope of the combined current profiles is identified based only on the duration of the predetermined period and the intensity variation of the plurality of LED or LED groups corresponding to the desired illumination characteristic applied during the transmission, 
 wherein the combined profile has a high current period and a low current period during each predetermined period, 
 wherein each predetermined period represents a single symbol. 
 
     
     
       31. The control unit according to  claim 30 , wherein the control unit is further configured to:
 receive a further set-point representing a different desired illumination characteristic, determine a further current profile for one or more LEDs or LED groups of the plurality of LEDs to generate the different desired illumination characteristic represented by the further set-point; 
 determine one or more intermediate current profiles for one or more LEDs or LED groups of the plurality of LEDs or LED groups, and 
 determine output control signals for the LED driver to sequentially drive the plurality of LEDs or LED groups according to: 
 the current profiles when transmitting a first code word; 
 the one or more intermediate current profiles, when transmitting a respective one or more further code words, and 
 the further current profiles when transmitting a yet further code word. 
 
     
     
       32. The control unit according to  claim 31 , wherein each symbol is characterized by the predetermined period and at least two different intensities applied during the predetermined period. 
     
     
       33. The control unit according to  claim 32 , wherein each symbol is characterized by application of a comparatively high intensity during a first portion of the predetermined period, followed by application of a comparatively low intensity during a second portion of the predetermined period.